While in the shower today, I was struck by a random though (this happens very often) for a blog post.
In English, we have relatively clearly defined categories for words, the main ones being nouns, adjectives, adverbs, and verbs. Of course, there are fundamental processes for changing words from one class to another; verbs may become nouns ('run' -> 'running'); adjectives may become adverbs ('quick' -> 'quickly'); nouns may become adjectives ('beauty' -> 'beautiful'); and in processes that I'm not entirely sure are grammatically correct, verbs may become adjectives ('castrate' + 'sledgehammer' -> 'castrating sledgehammer') and nouns may become verbs (e.g. "Verbing weirds languages" - Calvin). However, there are lots of ways of designing languages that don't have such clear distinctions. For the sake of keeping this relatively brief, I'm going to restrict this post to dealing with adjectives.
To the best of my understanding, Chinese does not have a clear distinction between nouns, verbs, and adjectives. Chinese is a strongly analytic language: the position of a word in a sentence and other words around it determine what role it plays. Japanese borrowed many of these Chinese words, and uses them also in all three categories.
For a well-known example, the word 'baka'. Used alone, it could mean 'idiot', 'mistake', 'stupidity', or something trivial. However when combined with 'na' (a particle which makes a noun act like an adjective), it becomes an adjective (e.g. 'baka na inu' - 'stupid dog'; not to be confused with 'inu no baka' - 'dog's stupidity'). This is not so unlike English, as sometimes you can use 'of' in basically the same way the Japanese use 'na'. 'yakusoku' is similar. Used alone, it means 'promise', 'arrangement', or 'rule'. But when accompanied by the auxiliary verb 'suru', it becomes a verb (e.g. 'yakusoku suru' - 'to promise').
However, that's mainly used for Chinese loan-words and compound words (and I'd guess that's how you'd do verbing in Japanese). The Japanese language itself has a different mechanism for adjectives. Pure Japanese (ignoring words derived from Chinese) does not have (nor need) true adjectives. Rather, what we would consider adjectives are actually intransitive verbs. For example, 'warui' means 'to be bad/evil/inferior/unprofitable/wrong/at fault/sorry'. These 'adjectives' are conjugated in principle the same as verbs, but the suffixes are different (though there's some evidence from ancient writings that at one time they were the same; I believe they still are the same in Korean, a sister language of Japanese). So, if we wanted to say, for example, 'the dog is bad', we would say 'inu wa warui' (in Japanese the verb comes at the end of the sentence; 'wa' indicates the topic of the sentence).
However, it's possible for such words to also be used as adjectives. For example, 'warui inu' would mean something like 'bad dog'. How do we account for that? The nature of the Japanese and Korean languages accounts for this rather beautifully, actually. The key, here, is how they construct sentences and clauses. Japanese has no relative pronouns ('that', etc.; e.g. 'dog that loves Kaity'); Japanese relative clauses are formed by putting the clause in front of the noun the clause relates to. So, for example, 'dog which bites' would be 'kamitsuku inu' ('kamitsuku' is the verb 'bite'); actually, this, like much of the Japanese language, is a bit ambiguous, as it could also mean 'dog that is bitten'. Thus 'warui inu' would literally mean 'dog which is bad', having the same meaning as 'bad dog' (as we would use in English, rather than the relative clause form).
You'll notice that English has actually developed something similar. Consider the term I coined - 'holy castrating sledgehammer'. In this case, what is meant is 'sledgehammer which castrates'. Here, we use a different form of the verb to make it into an adjective, but the basic concept is the same.